1. Field of the Invention
The present invention relates to an actuator drive system and a fuel injection system having an actuator, which is driven by electrical energy stored in a charge circuit.
2. Description of Related Art
An example of an actuator drive system and a fuel injection system is shown in FIG. 5A. In the technology shown in FIG. 5A (for instance, which is disclosed in Unexamined Japanese Patent Application Publication No. H07-71639), a capacitor (a condenser) 44 of a charge circuit 41 stores a large amount of electrical energy (a high voltage). When an injector 3 is driven, the electrical energy stored in the capacitor 44 and electrical energy provided by a constant current circuit 42 are supplied to an electromagnetic valve 32 mounted on the injector 3. Thus, response of the electromagnetic valve 32 is improved, so response of the injector 3 is improved.
If a selection switch 43 disposed in an energization circuit of the injector 3 is turned on at command injection timing a1 (shown in FIG. 5B) to operate the injector 3, the electrical energy stored in the capacitor 44 and the electrical energy provided by the constant current circuit 42 are supplied to the injector 3 as shown by a curved line (an injection pulse signal) a2 in FIG. 5B indicating a driving current I. The timing a1 is timing for outputting a command signal to the injector 3. Thus, the injector 3 starts the injection at the target injection timing. The system shown in FIG. 5A energizes the injector 3 by a multi-switching method. A switch 47 separates the capacitor 44 if the driving current I reaches a predetermined current (a peak current).
At that time, since the electrical energy stored in the capacitor 44 is supplied to the injector 3, the capacitor 44 is discharged and a charging voltage V decreases as shown by a part a3 of a solid line indicating the charging voltage V in FIG. 5B.
A control device controlling the charging voltage V of the capacitor 44 monitors the charging voltage V. If the charging voltage V decreases from a specified value (a fully-charged voltage) Vf, the control device operates a charging unit 45 of the charge circuit 41 to increase the charging voltage V of the capacitor 44 to the specified value Vf. Thus, the charging voltage V of the capacitor 44 increases to the specified value Vf as shown by a part a4 of the solid line indicating the charging voltage V in FIG. 5B.
In recent years, in order to achieve prevention of engine vibration and engine noise, purification of exhaust gas, and improvement of engine output and gas mileage at the same time at a high level, it is required to perform multiple injections (a multi-injection) in a compression and expansion stroke of a cylinder (a period suitable for performing fuel injection for generating engine torque).
In the case where the multi-injection is not performed, the number of times of the injections is small. Therefore, there is an adequate period to charge the capacitor 44 after the capacitor 44 is discharged. However, if the multi-injection is performed, an interval between the injection and the next injection is shortened. In this case, there is a possibility that the next injection is started before the charging voltage V of the capacitor 44 reaches the specified value Vf.
If a certain level of the interval is provided between the command injection timing a1 and next command injection timing b1 as shown in FIG. 5B, the capacitor 44, which is discharged at the command injection timing a1, can be charged by the next command injection timing b1. If the selection switch 43 is turned on at the command injection timing b1, the electrical energy stored in the capacitor 44 and the electrical energy provided by the constant current circuit 42 are supplied to the injector 3 as shown by a curved line b2 in FIG. 5B indicating the driving current I. Thus, the injector 3 can perform a predetermined injection operation. More specifically, the injector 3 starts the injection at target injection timing and performs the injection for a target injection period.
Also in this case, the capacitor 44 is discharged and the charging voltage V decreases as shown by a part b3 of the solid line indicating the charging voltage V in FIG. 5B. Therefore, the charging operation is performed to increase the charging voltage V of the capacitor 44 to the specified value Vf as shown by a part b4 of the solid line indicating the charging voltage V in FIG. 5B.
However, an interval between the command injection timing b1 and next command injection timing c1 is short as shown in FIG. 5B. Therefore, there is a possibility that the command injection timing c1 is reached while the charging voltage V is increasing as shown by the part b4 of the solid line indicating the charging voltage V in FIG. 5B.
In such a case, if the selection switch 43 is turned on at the command injection timing c1, at which the capacitor 44 is still being charged, the electrical energy, which is stored in the capacitor 44 and is less than the specified value Vf, and the electrical energy provided by the constant current circuit 42 are supplied to the injector 3. As a result, the electrical energy supplied to the injector 3 in accordance with a pulse signal c2 of the driving current I in FIG. 5B is relatively low.
If the electrical energy supplied to the injector 3 decreases, the driving force of the electromagnetic valve 32 decreases and the response of the electromagnetic valve 32 is delayed. As a result, actual injection timing (timing when the fuel injection from the injector 3 is actually started) is delayed from the target injection timing.
If the actual injection timing is delayed, an actual injection period (a period in which the injector 3 actually injects the fuel) is shortened. As a result, the target injection quantity of the fuel cannot be injected.
In the system of the related art shown in FIG. 5A, which includes the constant current circuit 42 in addition to the charge circuit 41, the rising of the current at the time when the constant current circuit 42 starts outputting the current will be changed if a constant current switch 46 of the constant current circuit 42 is turned on when the driving voltage applied to the injector 3 is lower than the specified value. Accordingly, the electrical energy supplied to the injector 3 is also changed by the change in the rising of the current. Therefore, the response of the injector 3 is changed and the actual injection timing and the actual injection quantity are changed.
In order to solve the above problems, a method of increasing a capacity of the capacitor 44 to store excessive electrical energy in the capacitor 44 or a method of mounting a multiplicity of capacitors 44 so that the capacitors 44 correspond to the respective injections of the multi-injection can be employed. However, the body size of the charge circuit 41 will increase and the cost of the charge circuit 41 will increase.